1. Field of the Invention
The invention relates to an arrangement for for determining the impedance in the heart by way of the pacemaker electrode disposed in the ventricle chamber.
2. Background Information
In some cases it is favorable to determine the electrical impedance in the heart region, using measuring technology, during operation of pacemakers, particularly in connection with an adaptation of the stimulation rate to the instantaneous stress on the patient.
It is known, for example, to determine the cardiac stroke volume in the manner of impedance plethysmography, i.e., by means of a measurement of the impedance in the heart. To do this, in the simplest case two electrodes are inserted into the heart. If a current of a known magnitude flows through the cardiac volume via these electrodes, the impedance in the heart can be determined by means of a voltage measurement. A corresponding apparatus for measuring the ventricular volume is described in DE-36 29 587-A1. This type of arrangement is not suitable for use in pacemakers.
From EP-A-0 140 472, a pacemaker is known in which the impedance in the heart is measured by way of further electrodes disposed at the pacemaker electrode, and the stimulation rate is controlled with the stroke volume determined from this. In this case, a series of measurements is provided from whose average value the stroke volume is calculated, which however, has disadvantages.